1. Field of the Invention
This invention relates to a process for preparing 2,6-dichlorotoluene, and more particularly to a process wherein liquid para-toluenesulfonyl chloride is reacted wtih chlorine gas in the presence of a catalyst.
2. Related Information
Dichlorinated toluenes are important intermediates in the preparation of pharmaceuticals, dyes, pigments, rubber chemicals and other organic compounds. 2,6-dichlorotoluene is especially useful as an intermediate in the preparation of herbicides.
U.S. Pat. No. 4,006,195 issued to Gelfand, Feb. 1, 1977, discloses an improved process for the catalytic production of 2,4-dichlorotoluene by reacting liquid parachlorotoluene with chlorine in the presence of an antimony trichloride catalyst at a temperature from about 0.degree. C. to about 100.degree. C. and especially from about 20.degree. C. to about 70.degree. C. The reaction product is treated with anhydrous ammonia then the catalyst is removed by filtration prior to distillation which yields substantially pure 2,4-dichlorotoluene. This process neither discloses the preparation of 2,6-dichlorotoluene nor the use of liquid para-toluenesulfonyl chloride as a reagent.
Japanese Patent, Jpn. Kokai Tokkyo Koho JP No. 60/16965 A2 (85/16965), Jan. 28, 1985, Appl. 83/124691, July 11, 1983 cited in Chemical Abstracts as CA 103(3):22277t discloses the dechlorination of tricholoro-paratoluenesulfonic acid in sulfuric acid with cuprous or cupric compounds. Desulfonation yielded 98.5% 2,6-dichlorotoluene. This reference neither discloses the use of liquid paratoluenesulfonyl chloride and ammonium hydroxide nor the use of antimony trichloride, or ferric chloride catalysts.
PRODUCTION OF 2,3,6-TRICHLOROBENZOIC ACID BY LIQUIDPHASE CATALYTIC OXIDATION OF 2,3,6-TRICHLOROTOLUENE, F.F. Shcherbina, D. N. Tmenov, T. V. Lysukho, and N. P. Belous, Institute of Physicoorganic Chemistry and Coal Chemistry, Petrochemical Branch, Academy of Sciences of the Ukranian SSR, pages 2076-2078, translated from Zhurnal Prikladnoi Khimii, Vol. 53, No. 12, pp 2737-2740, December, 1980, discloses that para-toluenesulfonic acid and antimony trichloride in chloroform was heated to 70.degree.-80.degree. C. with agitation while chlorine was passed through the reaction mixture. After the solvent was distilled, 75% sulfuric acid was boiled with the residue which was later extracted with toluene. The toluene extract was washed with 5% alkali solution then the toluene was distilled off. The resulting product contained 1.4% dichlorotoluenes, 0.7% tetrachlorotoluenes, and 97.9% 2,3,6-trichlorotoluene. This reference primarily discloses the preparation of trichlorotoluene and utilizes a chloroform solvent in the catalyzed reaction.
W. Davis et al., J. CHEM. SOC. 119, 853 (1921), THE CUMULATIVE EFFECT OF THE CHLORINE ATOM AND THE METHYL AND SULFONYL CHLORIDE GROUPS ON SUBSTITUTION IN THE BENZENE NUCLEUS. PART 1. discloses the preparation of 2,6-dichloro-para-toluenesulfonyl chloride by chlorinating a fused mixture of 2-chloro-para-toluenesulfonyl chloride and antimony chloride at 67.degree.-75.degree. C. for 2 hours. This reference neither describes the use of para-toluenesulfonyl chloride nor the use of sulfuric acid and ammonium hydroxide.
U.S. Pat. No. 3,470,151 issued to Doyle et al., Sept. 30, 1969, discloses the preparation of 2,6-dichlorotoluene according to the procedure of W. Davis et al., J. Chem. Soc., 119, 853 (1921). In this preparation, a mixture of 3,5-dichloro-4-methylbenzenesulfonyl chloride and 50% sulfuric acid was refluxed until the solution became homogeneous. The solution was then distilled with superheated steam for 5 hours and the distillate extracted with chloroform. The extracts were washed with water and dried with calcium chloride, the filtrate being evaporated to remove the solvent. Distillation of the residual oil gave 2,6-dichlorotoluene. This reference neither describes the catalyzed chlorination of liquid para-toluenesulfonyl chloride nor the treatment with ammonium hydroxide.